Photoconductive compositions and elements

ABSTRACT

Photoconductive compositions and elements containing as photoconductors organometallic compounds derived from Group IIIa metals are described.

United States Patent Arthur L. Johnson Rochester, N.Y.

Aug. 27, 1968 Sept. 21, 1971 Eastman Kodak Company Rochester, N.Y.

Inventor Appl. No. Filed Patented Assignee PHOTOCONDUCTIVE COMPOSITIONS AND ELEMENTS 33 Claims, No Drawings References Cited UNITED STATES PATENTS 7/1957 Ubbelohde 96/1.5 X

1/1962 Walde i 260/429 X 12/1963 Schlesinger 96/1.6 7/1964 Davis et a1. 96/1.5

12/1964 Schlesinger 96/1.5 7/1965 Wicklatz et a1. 260/429 X 11/1968 Sekiet al. 260/448 Primary Examiner-Charles E. Van Horn Attorneys-William H. J. Kline, James R Frederick and Fred L. Denson ABSTRACT: Photoconductive compositions and elements containing as photoconductors organometallic compounds derived from Group IIIa metals are described.

PHGTOCONDUCTIVE COMPOSITIONS AND ELEMENTS This invention relates to electrophotography and in particular to photoconductive compositions and elements.

The process of xerography, as disclosed by Carlson in US. Pat. No. 2,297,691, employs an electrophotographic element comprising a support material bearing a coating of a normally insulating material whose electrical resistance varies with the amount of incident electromagnetic radiation it receives during an imagewise exposure. The element, commonly termed a photoconductive element, is first given a uniform surface charge. generally in the dark after a suitable period of dark adaptation. It is then exposed to a pattern of actinic radiation which has the effect of differentially reducing the potential of this surface charge in accordance with the relative energy contained in various parts of the radiation pattern. The differential surface charge or electrostatic latent image remaining on the electrophotographic element is then made visible by contacting the surface with a suitable electroscopic marking material. Such marking material or toner, whether contained in an insulating liquid or on a dry carrier, can be deposited on the exposed surface in accordance with either the charge pattern or in the absence of charge pattern as desired. Deposited marking material can then be either permanently fixed to the surface of the sensitive element by known means such as heat, pressure, solvent vapor, or the like, or transferred to a second element to which it can similarly be fixed. Likewise, the electrostatic latent image can be transferred to a second element and developed there.

, Various photoconductive insulating materials have been employed in the manufacture of electrophotographic elements. For example, vapors of selenium and vapors of selenium alloys deposited on a suitable support and particles of photoconductive zinc oxide held in a resinous, film-forming binder have found wide application in the present day document-copying applications.

Since the introduction of electrophotography, a great many organic compounds have also been screened for their photoconductive properties. As a result, a very large number of organic compounds have been known to possess some degree of photoconductivity. Many organic compounds have revealed a useful level of photoconduction and have been incorporated into photoconductive compositions.

Typical of these organic photoconductors are the triphenylamines and the triarylmethane leuco bases. Optically clear photoconductorcontaining elements having desirable electrophotographic properties can be especially useful in electrophotography. Such electrophotographic elements can be exposed through a transparent base if desired, thereby providing unusual flexibility in equipment design. Such compositions, when coated as a film or layer on a suitable support, also yield an element which is reusable; that is, it can be used to form subsequent images after residual toner from prior images has been removed by transfer and/or cleaning. Thus far, the selection of various compounds for incorporation into photoconductive compositions to form electrophotographic layers has proceeded on a compound-by-compound basis. Nothing as yet has been discovered from the large number of different photoconductive substances tested which permits effective prediction, and therefore selection of the particular compounds exhibiting the desired electrophotographic properties.

lt is, therefore, an object of this invention to provide a novel class of photoconductors having high photosensitivity when electrically charged.

it is another object to provide novel photoconductor-containing compositions which exhibit high electrical speeds.

It is also an object to provide novel photoconductor-containing compositions which can be positively and negatively charged.

it is another object to provide novel transparent electrophotographic elements having high-speed characteristics.

It is a further object of this invention to provide novel electrophotographic elements useful for producing images electrophotographically by reflex or bireflex processes.

These and other objects of this invention are accomplished with electrophotographic elements having coated thereon photoconductive compositions containing as photoconductors organometallic compounds having at least one amino-aryl substituent attached to a Group lIIa metal atom.

The metallic substituents of these organometallic photoconductors are Group Illa metals in accordance with the Periodic Table of the Elements (Handbook of Chemistry and Physics, 38th edition, pp. 394-) and include boron, aluminum. galli um, indium and thallium. The organometallic photoconductors of this invention can be substituted in the metallo nucleus with a wide variety of substituents but at least one of the sub stituents should be an amino-aryl radicaL'The amino radical can be positioned anywhere on the aromatic nucleus, but best results are obtained if the aryl moiety is a phenyl radical having the amino group in the 4 or para position. Typical substituents attached to the metal nucleus include the following:

a. a hydrogen atom;

b. an alkyl group including substituted alkyl groups such as an aralkyl group e.g., benzyl, a halo-alkyl group e.g., a chloromethylene group, and aminoalkyl group e.g., CH N(Et) etc.;

c. an aryl group such as phenyl, naphthyl, etc.; including substituted aryl groups'such as aminoaryl e.g.,

M being a Group "It: metal and R and R being any of the substituents set forth in a. through e. above.

Illustrative photoconductors of this invention preferably have the following structure:

Rt D NArM 2i... i

wherein:

D and E can be either a. a hydrogen atom;

b. an aryl group including substituted and unsubstituted aryl groups such as pheny], naphthyl, dialkylaminophenyl, dialkylaminonaphthyl, etc.;

c. an alkyl group having 1 to 8 carbon atoms;

d. an alkoxy group having I to 8 carbon atoms;

e. an aryloxy group such as a phenyloxy group or;

f. an amino group e.g.,

R and R each being a hydrogen atom, an alkyl group or an aryl group;

Ar is an arylene group including a substituted arylene group e.g., a phenylene group, a naphthylene group, an alkylphenylene group, a halophenylene group, etc.;

M is a Group Illa metal;

R and R can be either a. a hydrogen atom,

b. an alkyl group having I to 8 carbon atoms or c. an aryl group such as a phenyl or naphthyl group Particularly improved results are obtained when those photoconductors having the following structure are used:

R] T X D R and R each being a hydrogen atom, an alkyl group having 1 to 8 carbon atoms or an aryl group such as phenyl or naphthyl. X, T and Z can be the same or different and can be positioned in the 2, 3, or 6 positions on the phenylene ring.

Some typical organometallic photoconductors of this invention include:

TABLE I Tri-p-diethylaminophenylborane Tri-p-diphenylaminophenylborane Tri-p-methylaminophenylgallium Methyl-phenyl-p-diethylaminophenylborane 2 Napthyl-p-dimethylaminophenylborane p-Dipropylaminophenylborane Di-p-diethylaminophenylborane Ethoxy-p-dimethylaminophenyl aluminum hydride Diphenoxy-p-dibutylaminophenyl aluminum 10. Tri-(2,b-climethy14-diethylaminophenyl)indium 2-chloro-4-dimethylaminophenyl gallium hydride Tri-(2,6-diphenozy4-diethylaminophenyl)thallium Tri-(2,6-dimethoxy-4-dimethylaminophenyl )thallium Diphenylamino-p-diethylaminophenylborane Dimesityl-4-dimethylaminonaphthylborane Dimesityl-4-dimethylaminophenylborane Dimesity1-(3,5-dimethyi-4-methoxyphenyl)borane Dimesityl-4-diphenylaminophenylborane 1,2Bis( p-diethylaminophenyl)diborane 1-Phenyl-2-methyldiborane Electrophotographic elements of the invention can be prepared with the photoconducting compounds of the invention in the usual manner, i.e., by blending a dispersion or solution or a photoconductive compound together with a binder, when necessary or desirable, and coating or forming a selfsupporting layer with the photoconductor-containing material. Mixtures of the photoconductors described herein can be employed. Likewise, other photoconductors known in the art can be combined with the present photoconductors. In addition, supplemental materials useful for changing the spectral May 10, 1966; fluorenes, such as 7,12-dioxo-13- dibenzo(a,h)flourene, 5,10-dioxo-4a,1 1 diazaben2o( b)fluorene, 3, l 3-dioxo-7-oxadibenzo(b,g)fluorene, trinitrofluorenonc, tetranitrofluorenone and the like; aromatic nitro compounds of U.S. Pat. No. 2,610,120; anthrones of U.S. Pat. No. 2,670,285; quinones of U.S. Pat No. 2,670,286; benzophenones of U.S. Pat. No. 2,670,287; thiazoles of U.S. Pat No. 2,732,301; mineral acids; carboxylic acids, such as maleic acid, dichloroacetic acid, and salicylic acid; sulfonic and phosphoric acids; and various dyes such as triphenylmethane, diarylmethane, thiazine, azine, oxazine, xanthene, phthalein, acridine, azo, anthraquinone dyes and many other suitable sensitizing dyes. The preferred sensitizers for use with the compounds of this invention are pyrylium salts including selenapyrylium and thiapryrlium salts, fluorenes, carboxylic acids, and triphenylmethane dyes.

Where a sensitizing compound is to be used within a photoconductive layer as disclosed herein it is conventional practice to mix a suitable amount of the sensitizing com-- pounds with the coating composition so that, after thorough mixing the sensitizing compound is uniformly distributed throughout the desired layer of the coated element. In preparing the photoconducting layers, no sensitizing compound is needed for the layer to exhibit photoconductivity. The lower limit of sensitizer required in a particular photoconductive layer is, therefore, zero. However, since relatively minor amounts of sensitizing compound give substantial improvement in the electrophotographic speed of such layers, the use of some sensitizer is preferred. The amount of sensitizer that can be added to a photoconductor incorporating layer to give effective increases in speed can vary widely. The optimum concentration in any given case will vary with the specific photoconductor and sensitizing compound used. In general, substantial speed gains can be obtained where an appropriate sensitizer is added in a concentration range from about 0.000l to about 30 percent by weight based on the weight of the filmforming coating composition. Normally, a sensitizer is added to the coating composition in an amount by weight from about 0.005 to about 5.0 percent by weight of the total coating composition.

Preferred binders for use in preparing the present photoconductive layers are film-forming, hydrophobic polymeric binders having fairly high dielectric strength which are good electrically insulating film-fonning vehicles. Materials of this type comprise.styrene-butadiene copolymers; silicone resins; styrene-alkyd resins; silicone-alkyd resins; soyaalkyd resins; poly (vinyl chloride); poly(vinylidene chloride); vinylidene chloride-acrylonitrile copolymers; poly(vinyl acetate); vinyl acetate-vinyl chloride copolymers; poly(vinyl acetals), such as poly(vinyl butyral); polyacrylic and methacrylic esters, such as poly(methylmethacrylate), poly(nbutylmethacrylate), poly(isobutyl methacrylate), etc.; polystyrene; nitrated polystyrene; polymethylstyrene; isobutylene polymers; polyesters, such as poly (ethylenealkaryloxyalkylene terephthalate); phenoformaldehyde resins; ketone resins; polyamides; polycarbonates; polythiocarbonates; poly(ethyleneglycol-co-bishydroxyethoxyphenol propane terephthalate); copolymers of vinyl haloarylates and vinyl acetate such as poly(vinyl-m-bromobenzoate-covinylacetate); etc. Methods of making resins of this type have been described in the prior art, for example, styrene-alkyd resins can be prepared according to the method described in U.S. Pat. Nos. 2,361,019 and 2,258,423. Suitable resins of the type contem plated for use in the photoconductive layers of the invention are sold under such tradenames as Vitel PE-lOl, Cymac, Pic

copale 100, Saran F-220, Lexan 105 and Lexan 145. Other types of binders which can be used in the photoconductive layers of the invention include such materials as paraffin, mineral waxes, etc. 7

Solvents of choice for preparing coating compositions of the present invention can include a number of solvents such as benzene, toluene, acetone, Z-butanone, chlorinated hydrocarbons, e.g., methylene chloride, ethylene chloride, etc., ethers e.g., tetrahydrofuran, or mixtures of these solvents, etc.

In preparing the coating composition useful results are obtained where the photoconductor substance is present in an amount equal to at least about lweight percent of the coating composition. The upper limit in the amount of photoconductor substance present can be widely varied in accordance with usual practice. In those cases where a binder is employed, it is normally required that tee photoconductor substance be present in an amount from about lweight percent of the coating composition to about 99weight percent of the coating composition. A preferred weight range for the photoconductor substance in the coating composition is from about l0weight percent to about 60weight percent.

Coating thicknesses of the photoconductive composition on a support can vary widely. Normally, a coating in the range of about 0.001 inch to about 0.01 inch before drying is useful for the practice of this invention. The preferred range of coating thickness was found to be in the range from about 0.002 inch to about 0.006 inch before drying although useful results can be obtained outside of this range.

Suitable supporting materials for coating the photoconductive layers of the present invention can include any of a wide variety of electrically conducting supports, for example, paper (at a relative humidity above percent); aluminum-paper laminates; metal foil such as aluminum foil, zinc foil, etc.; metal plates, such as aluminum, copper, zinc, brass, and galvanized plates; vapor deposited metal layers such as silver or aluminum and the like. An especially useful conducting support can be prepared by coating a support material such as polyethylene terephthalate with a layer containing a semiconductor dispersed in a resin. Such conducting layers both with and without insulating barrier layers are described in US. Pat. N o. 3,245,833. Likewise, a suitable conducting coating can be prepared from the sodium salt of a carboxyester lactone maleic anhydride and a vinyl acetate polymer. Such kinds of conducting layers and methods for their optimum preparation and use are disclosed in U.S. Pat. Nos. 3,007,901 and 3,267,807.

The elements of the present invention can be employed in any of the well-known electrophotographic processes which require photoconductive layers. One such process is the aforementioned xerographic process. As previously explained, in a process of this type the electrophotographic element is given a blanket electrostatic charge by placing the same under a corona discharge which serves to give a uniform charge to the surface of the photoconductive layer. This charge is retained by the layer owing to the substantial insulating property of the layer, i.e., the low conductivity of the layer in the dark. The electrostatic charge formed on the surface of the photoconducting layer is then selectively dissipated from the surface of the layer by exposure to light through an image-bearing transparency by a conventional exposure operation such as, for example, by contact printing technique, or by lens projection of an image, etc., to form a latent image in the photoconducting layer. By exposure of the surface in this manner, a charged patten is created by virtue of the fact that light causes the charge to be conducted away in proportion to the intensity of the illumination in a particular area. The charge pattern remaining after exposure is then developed, i.e., rendered visible, by treatment with a medium comprising electrostatically attractable particles having optical density. The developing electrostatically attractable particles can be in the form of a dust, e.g., powder, pigment in a resinous carrier, i.e., toner, or a liquid developer may be used in which the developing particles are carried in an electrically insulating liquid carrier. Methods of development of this type are widely known and pies which include preferred embodiments thereof.

have been described in the patent literature in such patents, for example, as US. Pat. No. 2,297,691 and in Australian Pat. 212,315. In processes of electrophotographic reproduction such as in xerography, by selecting a developing particle which has as one of its components, a low-melting resin, it is possible to treat the developed photoconductive material with heat and cause the powder to adhere permanently to the surface of the photoconductive layer. In other cases, a transfer of the image formed on the photoconductive layer can be made to a second support, which would then become the final print. Techniques of the type indicated are well known in the art and have been described in a number of U5. and foreign patents, such as U.S. Pats. Nos. 2,297,69l and 2,55 L582, and in RCA Review, vol. 15(1954 pages 469-484.

The present invention is not limited to any particular mode of use of the new electrophotographic materials, and the exposure technique, the charging method, the transfer (if any), the developing method, and the fixing method as well as the materials used in these methods can be selected and adapted to the requirements of any particular technique.

Electrophotographic materials according to the present invention can be applied to reproduction techniques wherein different kinds of radiations, i.e., electromagnetic radiations as well as nuclear radiations, can be used. For this reason, it is pointed out herein that although materials according to the invention are mainly intended for use in connection with methods comprising an exposure, the term electrophotograhpy wherever appearing in the description and the claims, is to be interpreted broadly and understood to comprise both xerography and xeroradiography.

The invention is further illustrated by the following exam- EXAMPLE I Tri-p-diethylaminophenylborane is separately incorporated into a coating dope have the following composition:

a. 0.25 gram of Lexan (trade name of General Electric Company for poly(4,4-isopropylidenediphenylcarbonate as a binder b. 0.25 gram of tri-p-diethylaminophenylborane as a photoconductor c. 4.5 grams of a 0.0029 g./ml. solution of [4-(pdimethylaminophenyl)-2,6-diphenylthiapyrylium perchlorate] in methylene chloride as a sensitizer for the photoconductor d. 7.7 grams of a composition 1 F. These electrophotographic elements are charged under a positive or negative corona source until the surface potentials, as measured by an electrometer probe,

I reach about 600 volts. They are then subjected to exposure from behind a stepped density gray scale to a 3000 K. tungsten source. The exposure causes reduction of the surface potentials of the elements under each step of the gray scale from their initial potential, V, to some lower potential, V whose exact value depends on the actual amount of exposure in meter-candle-seconds received by the areas. The results of the measurements are plotted on a graph ofsurface potential V vs. log ex posure for each step, The shoulder speed is the numerical expression of 10' mal- 65.

reduce the 600-volt-churged surface potential by I00 volts. The toe speed is the numcrlcul expression of IO multiplied by the reciprocal of the exposure in meters tiplied by the reciprocal of the exposure in mcter-candle-scconds required to candle-seconds required to reduce the ti0l)-volt-charged surface potential to I00 volts. The above composition has positive and negative shoulder speeds of 2.500

and 3.400 respectively. Positive and negative toe speeds are 250 and 900 respectively.

EXAMPLE ll perchlorate. Positive and negative shoulder and toe speeds remain virtually unchanged. Similarly good results are obtained when 2,4-bis( 4-ethylphenyl )-6-( 4-styrylstyryl )pyrylium perchlorate is used.

EXAMPLE III Coating dopes are prepared in the manner described in example I using the materials set forth therein. The photoconductors employed are compounds lin Table I. In a darkened room, the surface of each of the photoconductive layers so prepared is charged to a potential of about +600 volts under a corona charger. The layer is then covered with a transparent sheet bearing a pattern of opaque and lighttransmitting areas and exposed to the radiation from an incandescent lamp with an illumination intensity of about 75 metercandles for 12 seconds. The resulting electrostatic latent image is developed in the usual manner by cascading over the surface of the layer a mixture of negatively charged black thermoplastic toner particles on glass beads functioning as carriers for the toner particles. A good reproduction of the pattern results in each instance. Similar results are obtained using a liquid developer.

The photoconducting compounds of this invention can generally be prepared by synthesis familiar to those skilled in the art. Typically, an intermediate Grignard or lithium derivative is prepared containing the desired substitutents by conventional methods. The final product is prepared by reacting stoichiometric quantities of the intermediate with a Group lIla metal halide or a Group Illa metal halide containing the substituents desired in the final compound. A typical preparation is set forth below. Example IV describes the preparation of a typical tri-dialkylaminophenylborane wherein the alkyl moiety typically has 1 to 8 carbon atoms. The described procedure can be utilized to prepare the related organometallic compounds described above.

EXAMPLE IV A flask containing 17.2 g. (0.72 moles) of magnesium is heated at 100 C. for 1 hour, cooled to below 60 C. and treated with a ml. portion of a solution of 55.2 g. (0.24 moles) of distilled p-bromo-N,N-diethylaniline in 240 ml. of dry tetrahydrofuran (distilled from calcium hydride). The reaction starts on heating under reflux. The remainder of the solution is added at such a rate as to maintain reflux. The resulting dark brown mixture is heated under reflux for 1 hour and then treated dropwise with a solution of 11.4 g. (0.08 moles) of boron trifluoride-ethyl ether in 100 ml. of dry tetrahydrofuran. The resulting mixture is heated under reflux for 2 hours. The solution is removed from unreacted magnesium and treated with ice and a dilute ammonium chloride solution. The solid which precipitates is dried in air at room temperature and purified by recrystallizing from boiling acetonitrile. The solid which results is dried in air at room temperature. 1.79 g. of white crystalline solid tri-pdiethylaminophenylborane having a melting point of 242-27 3 C. are obtained.

Found: C,79.1; l-I,9. l; B,2.5; N,9.3

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

lclaim:

l. A photoconductive composition comprising an electrically insulating, polymeric binder having dispersed therein a photoconductor selected from the group consisting of a Group Illa organometallic compound having at least one amino-aryl group attached to a Group Illa metal atom.

2. The photoconductive composition as defined in claim 1 in which a sensitizer for said photoconductor is also present.

3. A photoconductive composition comprising a photoconductor which is a Group Illa organometallic compound having attached to a Group Illa metal atom (l) at least one aminoaryl group and (2) at least one substituent selected from the group consisting of a hydrogen atom, an alkyl group, an aryl group, a Group Illa organometallic group, an alkoxy group, an aryloxy group and an amino group and a sensitizer for said photoconductor.

4. The photoconductive composition as defined in claim 3 wherein:

Ar is an arylene group;

D and E are each selected from the group consisting of an aryl group, an alkyl group, a hydrogen atom, an alkoxy group, an aryloxy group and an amino group;

M is a Group Illa metal; and

R and R are each selected from the group consisting of an alkyl group, an aryl group and a hydrogen atom, and a sensitizer for said photoconductor.

9. The photoconductive composition as defined in claim 8 wherein M is boron.

10. The photoconductive composition as defined in claim 8 wherein R and R are each alkyl groups.

11. The photoconductive composition as defined in claim 8 wherein D and E are each p-dialkylaminophenyl groups.

12. The photoconductive composition as defined in claim 8 wherein Ar is a phenylene group.

13. The photoconductive composition as defined in claim 8 wherein the sensitizer is a pyrylium salt.

14. A photoconductive composition photoconductor represented by the formula:

comprising a wherein:

R and R are each selected from the group consisting of an alkyl group, an aryl group and hydrogen; D and E are each selected from the group consisting of an aryl group, an alkyl group, hydrogen, an alkoxy group, an aryloxy group and an amino group; M is a Group llla metal; and X, T and Z are each selected from the group consisting of hydrogen, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, a halogen atom and an amino group, and a sensitizer for said photoconductor. 15. The photoconductive composition as defined in claim 14 wherein M is boron.

16. The photoconductive composition as defined in claim 14 wherein D and E are each a p-dialkylaminophenyl group.

17. The photoconductive composition as defined in claim 14 wherein R and R are each an alkyl group.

18. The photoconductive composition as defined in claim 14 wherein the sensitizer is a pyrylium salt.

19. An electrophotographic element comprising a support having coated thereon a composition comprising a photoconductor which is a Group Illa organometallic compound having at least one amino-aryl group attached to a Group Illa metal atom.

20. An electrophotographic element comprising a support having coated thereon a composition comprising a photoconductor which is a Group Illa organometallic compound having attached to a Group Illa metal atom (1) at least one aminoaryl group and (2) at least one substituent selected from the group consisting of a hydrogen atom, an alkyl group, an aryl group, a Group Illa organometallic group, an alkoxy group an aryloxy group and an amino group.

21. The electrophotographic element as defined in claim wherein the Group IIIa organometallic compound is borane.

22. The electrophotographic element as defined in claim 20 wherein the Group Illa organometallic compound is a p-dialkylaminophenylborane.

23. The electrophotographic element as defined in claim 20 wherein the Group Illa organometallic compound is pdiethylaminophenylborane.

24. An electrophotographic element comprising a support having coated thereon a composition comprising a photoconductor represented by the formula:

wherein:

Ar is an arylene group;

D and E are each selected from the group consisting of an aryl group, an alkyl group, a hydrogen atom, an alkoxy group, an aryloxy group and an amino group;

M is a Group Illa metal; and

R and R are each selected from the group consisting of an alkyl group, and aryl group and a hydrogen atom.

25. The electrophotographic element as defined in claim 24 wherein M is boron.

26. The electrophotographic element as defined in claim 24 wherein R and R are each an alkyl group.

27. The electrophotographic element as defined in claim 24 wherein D and E are each a p-dialkylaminophenyl group.

28. The electrophotographic element as defined in claim 24 wherein Ar is a phenylene group.

29. An electrophotographic element comprising a support having coated thereon a composition comprising a photoconductor represented by the formula:

wherein:

R and R are each selected from the group consisting of an alkyl group, an aryl group and hydrogen;

D and E are each selected from the group consisting of an aryl group, an alkyl group, hydrogen, an alkoxy group, an aryloxy group and an amino group;

M is a Group Illa metal; and

X, T and Z are each selected from the group consisting of hydrogen, an alkyl group an aryl group, an alkoxy group, an aryloxy group, a halogen atom and an amino group.

30. The electrophotographic element as defined in claim 29 wherein M is boron.

31. The electrophotographic element as defined in claim 30 wherein D and E are each a pdialkylaminophenyl group.

32. The electrophotographic element as defined in claim 30 wherein R, and R are each an alkyl group.

33. An electrophotographic element comprising a support having coated thereon a photoconductive composition comprising 10 to about 60 weight percent of tri-pdiethylaminophenylborane as a photoconductor, 0.005 to about 5.0 weight percent of [4-(p-diethylaminophenyl)-2,6- diphenylthiapyrylium perchlorate] as a sensitizer and a polymeric binder for said photoconductor. 

2. The photoconductive composition as defined in claim 1 in which a sensitizer for said photoconductor is also present.
 3. A photoconductive composition comprising a photoconductor which is a Group IIIa organometallic compound having attached to a Group IIIa metal atom (1) at least one amino-aryl group and (2) at least one substituent selected from the group consisting of a hydrogen atom, an alkyl group, an aryl group, a Group IIIa organometallic group, an alkoxy group, an aryloxy group and an amino group and a sensitizer for said photoconductor.
 4. The photoconductive composition as defined in claim 3 wherein the Group IIIa organometallic compound is a borane.
 5. The photoconductive composition as defined in claim 3 wherein the Group IIIa organometallic compound is a p-dialkylaminophenylborane.
 6. The photoconductive composition as defined in claim 3 wherein the Group IIIa organometallic compound is p-diethyl-aminophenylborane.
 7. The photoconductive composition as defined in claim 3 wherein the sensitizer is a pyrylium salt.
 8. A photoconductive composition comprising a photoconductor represented by the formula:
 9. The photoconductive composition as defined in claim 8 wherein M is boron.
 10. The photoconductive composition as defined in claim 8 wherein R1 and R2 are each alkyl groups.
 11. The photoconductive composition as defined in claim 8 wherein D and E are each p-dialkylaminophenyl groups.
 12. The photoconductive composition as defined in claim 8 wherein Ar is a phenylene group.
 13. The photoconductive composition as defined in claim 8 wherein the sensitizer is a pyrylium salt.
 14. A photoconductive composition comprising a photoconductor represented by the formula:
 15. The photoconductive composition as defined in claim 14 wherein M is boron.
 16. The photoconductive composition as defined in claim 14 wherein D and E are each a p-dialkylaminophenyl group.
 17. The photoconductive composition as defined in claim 14 wherein R1 and R2 are each an alkyl group.
 18. The photoconductive composition as defined in claim 14 wherein the sensitizer is a pyrylium salt.
 19. An electrophotographic element comprising a support having coated thereon a composition comprising a photoconductor which is a Group IIIa organometallic compound having at least one amino-aryl group attached to a Group IIIa metal atom.
 20. An electRophotographic element comprising a support having coated thereon a composition comprising a photoconductor which is a Group IIIa organometallic compound having attached to a Group IIIa metal atom (1) at least one amino-aryl group and (2) at least one substituent selected from the group consisting of a hydrogen atom, an alkyl group, an aryl group, a Group IIIa organometallic group, an alkoxy group an aryloxy group and an amino group.
 21. The electrophotographic element as defined in claim 20 wherein the Group IIIa organometallic compound is borane.
 22. The electrophotographic element as defined in claim 20 wherein the Group IIIa organometallic compound is a p-dialkylaminophenylborane.
 23. The electrophotographic element as defined in claim 20 wherein the Group IIIa organometallic compound is p-diethylaminophenylborane.
 24. An electrophotographic element comprising a support having coated thereon a composition comprising a photoconductor represented by the formula:
 25. The electrophotographic element as defined in claim 24 wherein M is boron.
 26. The electrophotographic element as defined in claim 24 wherein R1 and R2 are each an alkyl group.
 27. The electrophotographic element as defined in claim 24 wherein D and E are each a p-dialkylaminophenyl group.
 28. The electrophotographic element as defined in claim 24 wherein Ar is a phenylene group.
 29. An electrophotographic element comprising a support having coated thereon a composition comprising a photoconductor represented by the formula:
 30. The electrophotographic element as defined in claim 29 wherein M is boron.
 31. The electrophotographic element as defined in claim 30 wherein D and E are each a pdialkylaminophenyl group.
 32. The electrophotographic element as defined in claim 30 wherein R1 and R2 are each an alkyl group.
 33. An electrophotographic element comprising a support having coated thereon a photoconductive composition comprising 10 to about 60 weight percent of tri-p-diethylaminophenylborane as a photoconductor, 0.005 to about 5.0 weight percent of (4-(p-diethylaminophenyl)-2,6-diphenylthiapyrylium perchlorate) as a sensitizer and a polymeric binder for said photoconductor. 